1. Field of the Invention
This invention relates to an attitude stabilization control system for a legged mobile robot.
2. Description of the Prior Art
Legged mobile robots, in particular legged mobile robots using biped locomotion, are taught by Japanese Laid-open Patent Publication Nos. 62(1987)-97005 and 63(1988)-150176. A general discussion of robots, including legged mobile robots, can be found in Robotics Handbook, Robotic Society of Japan, Oct. 20, 1990.
The stability of legged mobile robots, in particular legged mobile robots using biped locomotion, is intrinsically low. Thus when such a robot is acted on by external forces (disturbance), its attitude easily becomes unstable. Because of this, it is necessary to control the robot's attitude on the basis of the detected inclinatory angle and angular velocity of the robot's trunk. The assignee earlier proposed a technique for enabling such control in Japanese Laid-open Patent Publication No. 4(1992)-201,187 (which was filed in the United States on Nov. 27, 1991 under the Ser. No. 07/799,367 and filed in the EPO on the same date under the number of 91310964.1). In the proposed system, a number of candidate footfall positions are established beforehand, one of the candidates is selected and the target walking pattern (gait) is switched during the control cycles of each walking step. This control has the following disadvantage. Once ground contactability has been diminished owing to attitude destabilization which causes the ZMP (zero moment point; the center of gravity at which only the vertical ground reaction force acts) to shift to near the limit of the range within which it can exist, it cannot therefore be promptly restored because the ZMP remains near its limit until the attitude is restored by correcting the walking pattern in the next step.